This invention relates to high pressure storage of waste gas produced in operation of a space vehicle such as a space station, and is particularly concerned with procedure for avoiding stress corrosion cracking of metal containers employed for storing pressurized waste gas containing corrosive contaminants.
In space station systems different laboratory modules on the space station are designed for carrying out a variety of experiments, and generate a mixed waste gas composed primarily of nitrogen, carbon dioxide, oxygen and inert gases. The mixed waste gas will also contain a wide variety of trace contaminant vapors and particles including organic and inorganic acids and bases and organic solvents, and halogens, generated from the experiments performed in the laboratory modules on the space station. Such waste gas can be removed, stored and propulsively vented through resistojets as part of a supplemental reboost propellant system for the space station. Thus, a substantial amount of primary reboost propellant is saved by using waste gases for supplemental reboost.
In the mixed waste gas system which is directly connected to the space station, the mixed waste gas is stored at high pressures of about 1000 to about 1100 psi. Such high pressure storage of mixed waste gases containing an uncertain mixture of chemical contaminants has caused grave concerns in regard to material reliability, corrosion and particularly stress corrosion cracking of metal storage containers and hardware, in the high pressure areas of the system.
Concentrations and mixtures of gases and contaminants will constantly change over the long period, e.g. 30 year, operation of the space station. Such a gas environment renders it very difficult to characterize material behavior with respect to corrosion and stress corrosion cracking resistance. To applicant's knowledge, no engineering metal that is compatible with all potential contaminants of the waste gas mixture is presently available, and there is potential danger of an unexpected, catastrophic failure of an all metal pressure vessel caused by stress corrosion cracking resulting from an unpredictable waste gas/contaminant environment. Because of such stress corrosion cracking concerns, an alternative to the all-metal pressure vessel for high pressure waste gas storage is required.
Composite pressure vessels with metal liners operating in compression are known. Thus, U.S. Pat. No. 3,969,812 discloses a method of producing an overwrapped composite pressure vessel which induces a compressive prestress into a metal liner by pressurizing the vessel beyond the elastic limit of the liner after overwrapping the liner, elastically unloading the liner by reducing the pressure, and compressing the liner with the filament overwrap. U.S. Pat. No. 3,240,644 is also exemplary of a method of making pressure vessels formed by winding layers of resin coated filaments on a metal shell, curing the resin and subjecting the interior of the shell to fluid pressure to expand the shell so as to establish a pre-stress in the cylindrical wall section.
It is an object of the present invention to provide a method for storing waste gases in a pressure vessel having a metal liner so as to provide stress corrosion cracking resistance of the liner.
Another object is to provide procedure for storing pressurized waste gas containing contaminants from a space station in a pressure vessel having a metal liner, over extended periods of storage while preventing stress corrosion cracking of the metal liner and avoiding the danger of catastrophic failure of the pressure vessel.
A still further object of the invention is the provision of an effective method for storing gas mixtures containing corrosive contaminants in pressure vessels other than all-metal pressure vessels under conditions to prevent stress corrosion cracking and the danger of catastrophic failure of an all-metal pressure vessel.
Other objects and advantages will appear hereinafter.